Usually to join someone's LAN server you just need to know his IP address. Naturally, that's assuming that he hasn't close his LAN with help of sv_lan 1 cvar (our LAN server uses sv_lan 0 by default, you can change it in cstrike\addons\amxmodx\configs\amxx.cfg). Besides, server owner can set a password for joining.

You can find out your own IP on https://www.myip.com or by typing in Windows command line ipconfig - you will see information about your connection including IPv4 Adress.

However there are cases when you cannot connect to the server like this (closed ports or bad configuration of router etc), so avoid racking your brains you can simply create your own virtual network with Hamachi (download).

Just click Next to install it (and don't choose to install additional stuff if you don't need it). This is how main window looks like:


As program suggests, click the Power button. Login windows pops up:


Enter your real email and think of a password, then you'll need to go to your email and confirm registration. If you're registered already, but cannot recall the password, click Forgot your password button and follow instructions.

Now then Power button is pressed, you can see the IP that you will have in virtual network (in my case it's 25.77.182.179). Also there is your computer name (mine is PC-Lite).

If you want to create your own network, click Create a new network button, new window will pop up:


Type in the any name of your network (someone maybe is already using it, in that case just choose another one) and password two times. The click Create, and it's done.
Now let's suppose your friend has created his own network with Hamachi. To join an existing network you just need to know its name and password. There is a limit of the number of participants in one network, so if there are no places left, you won't be able to join.


As you can see, he has the maximum of 5 places in free version of Hamachi, and 4 of them are occupied (you are not shown in the list). If he would want to allow more than 5 people join him, he just needs to create one more network.

Next you want to connect to his server in CS. Put a cursor on the name of his network. You will see who from the list is the owner. Right click on the owner and choose Copy IPv4 address:


In CS open console and paste IP, that you've just copied, after connect command:


That's it! Also you can change some settings in System -> Preferences menu:


By default Hamachi is starting with Windows, and there is no option in Preferences for disabling that. But if you really want to do it, then in your Windows right click on Computer, choose Manage -> Services and Applications -> Services, find LogMeIn Hamachi Tunneling Engine, double click it and set Startup Type to Manual: